I'm seeing a lot of nonsense about boosting the immune system lately, so here's a far-too-long thread on what "boosting the immune system" really means and why 1) you can't and 2) it's not smart.

Classically we regard the immune system as being a network of molecules, cells, and organs responsible from protecting us against pathogens (disease-causing microbes). But how does it do that?

The immune system has to have a means of being able to tell apart self-antigens from nonself-antigens so that it doesn't respond to the wrong ones. This is called self-tolerance and it's much trickier than you may be aware.

Self-tolerance has two layers: central tolerance and peripheral tolerance.
Central tolerance is where your B and T cells (cells that respond to specific antigens and then rapidly divide into clones in an immune response) are pre-programmed not to respond to self-antigen.

There are some problems, however. Your immune system has to be able to recognize self-antigen to function. Viruses hide within your cells and their antigens get presented on proteins called MHCs. T cells have receptors designed to recognize MHCs and the bound peptide.

However, MHCs also have to present self-antigen peptides with them. Viruses can completely disrupt cellular metabolism and basically stop antigen presentation. However- when cells don't have enough MHC proteins, they get destroyed by natural killer cells (no gif for this one):

In other words, a cell that doesn't present self-antigen is treated by the immune system as a cell that's been infected with a virus and killed.

To deal with this the immune system has evolved to only permit cells to escape their central tolerance education if they fall within a goldilocks zone of being able to recognize self-antigen but not respond strongly to it. The vast majority of cells fail this checkpoint.

However, sometimes self-reactive cells (cells specific to self-antigen) fall through the cracks and you end up releasing potentially dangerous cells with the potential to cause autoimmunity.

It's okay though! Autoreactive cells alone do not make an autoimmune disease. Many people have antibodies against self-antigen which never end up developing into an autoimmune disease.

That's because you have a second layer to self-tolerance called peripheral tolerance. Peripheral tolerance is arguably more important given how error prone central tolerance can be. Most of this boils down to a really important cell called the regulatory T cell (Treg).

Some of the T cells that respond strongly to self-antigen in the thymus (where central tolerance happens) become regulatory T cells. The regulatory T cells are responsible for controlling the immune system when it gets too eager to limit tissue damage.

They can also be induced in the course of an immune response. If a particular cell gets especially eager, the Tregs can even kill it: https://reader.elsevier.com/reader/sd/pii/S1074761309001976?token=1F27BECDAAD5962595AF71041FF8EFDBBE1839218D087F4F1C0E5283315350155585DFBE6B54FBF3B5F0DB23C42732E9

Tregs are very busy cells and they work very hard to prevent your autoreactive cells from causing disease. Don't make their job any harder by trying to boost your immune system.

There is only one immune booster I will ever endorse for the general public:

Thanks @DrJenGunter for being amazing and supplying me with the perfect gif https://twitter.com/i/status/1165641748703399936

Vaccines are not a general immune booster in the way that snake oil salesmen market their products. They enrich cells specific to antigens on disease-causing microbes so that if you encounter them you don't get sick.

They are also extensively evaluated for safety.

Don't buy into the hype of boosting your immune system. It's not going to work, and it's dangerous to try.

If you think your immune system doesn't work the way it should, you should talk to your doctor.